1. Field of the Invention
The present invention relates to a rechargeable lithium battery. More particularly, the present invention relates to a rechargeable lithium battery having improved structural and/or thermal stability.
2. Description of the Related Art
Rechargeable lithium batteries use materials that are capable of reversibly intercalating or deintercalating lithium ions as positive and negative active materials, and include an organic electrolyte solution or a polymer electrolyte between the positive and negative electrodes. Rechargeable lithium batteries generate electrical energy through an oxidation/reduction reaction during the intercalation/deintercalation of lithium ions at the positive and negative electrodes.
Chalcogenide compounds have been used for positive active materials. Chalcogenide compounds including composite metal oxides such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCoxO2 (0<x<1), LiMnO2, and so on have been researched.
Conventionally, lithium metals have been used as a negative active material for rechargeable lithium batteries. However, an explosion may be caused by a short circuit of the battery due to formation of dendrites when using a lithium metal. Therefore, carbonaceous materials such as amorphous carbon, crystalline carbon, etc., have recently been substituted as the negative active material in place of lithium metal. However, since carbon-based materials have a limited capacity, higher capacity materials are needed. Accordingly, to satisfy the high capacity requirement and to provide a high-capacity battery, metal-based negative active materials such as Si, Sn, and so on have been actively studied.
Since a rechargeable lithium battery including a non-carbon-based negative active material may have too much substrate expansion during charge and discharge, a core of a spirally wound electrode assembly especially in a cylindrical battery, may be severely misshapen. An electrode assembly 100 is formed by spirally winding positive and negative electrodes and having a separator interposed therebetween. The core, as shown in FIG. 1, includes a hollow space C in the center of the electrode assembly so that a pin may be inserted into the hollow space C. The hollow space is created after a mandril used for spirally winding the positive and negative electrodes is removed from the electrode assembly.
When a rechargeable lithium battery, in particular one including a non-carbon-based negative active material, incurs substrate expansion during repeated charge and discharge, the substrate expansion often occurs at the hollow space rather than at the periphery because the substrate is prevented from expanding by the can.
According to a conventional art, a center pin (mandril) is inserted to prevent expansion. However, an additional process of inserting a pin is therefore needed, making the manufacturing process complicated and thereby increasing the manufacturing cost. Accordingly, when an electrode includes a metal-based material that severely expands during charge and discharge, a jelly-roll type of electrode assembly may also be severely misshapen at its center, which deteriorates the cycle-life characteristic.